With the continuous development of semiconductor technologies, the critical dimension (CD) of the semiconductor devices has been continuously reduced. The reduction of the critical dimension of the semiconductor devices means that more transistors can be formed in a single chip. However, with the rapid reduction of the size of the transistors, the CMOS field-effect transistors are facing more challenges. For example, the short-channel effect is increased; the leakage current is increased; and the slope of the subthreshold voltage has the limitation of 60 mV/dec at the room temperature.
To adapt to the reduction of the size of the transistors, and to reduce the short-channel effect and reduce the slope of the subthreshold voltage, tunnel field-effect transistors (TFETs) have been developed. TFETs are a type of metal oxide semiconductor-controlled PIN diodes. TFETs utilize the quantum tunneling effect as the major mechanism to control the current; and a gate voltage to control the shape of the potential distribution inside the devices so as to affect the conditions to have the quantum tunneling effect. When the conditions are met, the TFET is turned on. When the conditions are not met, the current is rapidly reduced; and the TFET is turned off. The TFETs have the advantages of small slope of the subthreshold voltage and small off-current.
However, there is still a need to further reduce the slope of the subthreshold voltage and increase the on-currents of the TFETs. The disclosed methods and semiconductor structures are directed to solve one or more problems set forth above and other problems in the art.